Method and system for dissolving paraffin



Jan. 2, 1968 A. L; WALDRON METHOD AND SYSTEM FOR DISSOLVING PARAFFIN 2Sheets-Sheet 1 Filed July 28, 1965 FIGZ.

FIGI.

INVENTORZ ALTON L. WALDRON ATTYS,

Jan. 2, 1968 A. 1.. WALDRON METHOD AND SYSTEM FOR DISSOLVI NG PARAFFINFiled July 28, 1965 2 Sheets-sheaf 2 Pics.

2. I ATTYS.

United States Patent Ofilice 3,361,205 Patented Jan. 2, 1968 3,361,205METHOD AND SYSTEM FOR DISSOLVING PARAFFIN Alton L. Waldron, Annapolis,Md., assignor to I -Iydrasearch C0,, Inc., Annapolis, Md., a corporationof Maryland Filed July 28, 1965, Ser. No. 475,421 Claims. (Cl. 16641)ABSTRACT OF THE DISCLOSURE A method and apparatus for permitting thecleaning of parafiin deposits accumulated in the tubing string of an oilwell, without removing the tubing string. The apparatus includes a valvepositioned in the tubing string beneath the expected point ofaccumulation of paraffin and includes means in the valve responsive toan overpressure in the tubing string to permit communication between thetubing string and its exterior for dumping the oil above the valve intothe well casing. The valve also includes positive acting detent meanswhich maintains fluid communication between the tubing string and thewell casing until a predetermined lower pressure has been reached, thepredetermined lower pressure corresponding to the desired quantity ofoil superimposed of the valve in the tubing string. The method includesclosing off the tubing string and pumping an overpressure into thestring to cause the valve to open. Thereafter pressure is reduced bystopping the pump and a predetermined portion of the oil above the valveis permitted to drain into the well casing until the valve shuts off.Thereafter a solvent is introduced into the tubing string to dissolvethe parafi'in so that normal operation may once again be resumed.

The present invention relates to apparatus and a method for using thesame in oil wells and more particularly to a valve assembly and themethod of using the same which permits the treating of a well bore atpredetermined regions for removing paraifin deposits accumulatedtherein.

When an oil well has been in operation for a period of time, thesubterranean or reservoir pressure causing a flow of petroleum to thesurface gradually decreases, to the point that it becomes necessary torecover the remainder of the oil in the subterranean cavern by a pumpingoperation. When recovering the petroleum by pumping, paraffin depositsin the tubing string of the pumping line, usually at a predetermined andcalculable level, which deleteriously affects, curtails and even haltsthe pumping action. When this condition occurs, and in some Wells whichpump petroleum having a high paraffin content the condition occursrepeatedly at relatively short intervals, it is normally necessary topull the tubing string for the purpose of cleaning, or to resort tolaborious operations for cleaning the paratfin deposits while the tubingstring is in position. In either case the cleaning of the tubing stringby the methods abovedescribed results in lengthy shut-downs with, ofcourse, a concurrent financial loss.

The prior art has exhibited various means, including valve assembliesplaced in the tubing string, for perrnitting the placement in theso-called paraflin region (i.e. the depth at which paraflinaccumulations occur) of a solvent which will dissolve the parafiindeposits and permit further use of the well without removing the tubingstring or the sucker rod interiorly mounted therein. For example, in theAbbott Patent No. 3,016,094, which issued on Jan. 9, 1962, this valveassembly requires above-surface extensions reaching down to the valveassembly in order to effectuate a closing off of the tubing below theparafiin region. Because of the risk of corrosion by small quantities ofwater and sulphur in the petroleum, valves of this type have provedunacceptable over long periods of unattended service.

In view of the above, it is a principal object of the present inventionto provide a valve assembly for placement in the tubing string wherebyparaffin deposits thus occurring may be quickly and easily removedwithout the necessity for pulling the tubing string or sucker rod, andwith a minimum delay in the operation of the well.

Another object of the present invention is to provide a valve assemblywhereby a paraffin-removing agent such as a solvent may be effectivelyintroduced into the tubing string at the region of parafiin deposits foreffectively and economically removing the latter and restoring theproduction of the well.

Still another object of the present invention is to provide a valvewhich is automaticallyoperated and needs no connecting apparatusextending from the para ffin region to the surface.

Still another object of the present invention is to provide a valveassembly which may be placed in any part of the tubing string whereinthe predetermined parafiin region occurs, and which valve may beadjusted to operate at the desired depth in the tubing string.

Another object of the present invention is to provide a method ofautomatically dumping oil in the tubing string, above a novel valveassembly located therein, which method and apparatus permits theplacement of a solvent in the tubing string for dissolving the parafiinin the paraflin region.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a fragmentary side elevation view partially in sectionillustrating an oil Well having a valve con structed in accordance withthe present invention, positioned therein;

FIG. 2 is an enlarged fragmentary sectional view taken along line 2--2of FIG. 1;

FIG. 3 is a fragmentary sectional view of a portion of the exteriorcasing of the valve constructed in accordance with the present inventionand illustrating parafiin deposits above the valve;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2 and as if FIG.2 Were not in section;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2 and as if FIG.2 were not in section;

FIG. 6 is a sectional view taken along line 66 of FIG. 5;

FIG. 7 is a fragmentary sectional view similar to that illustrated inFIG. 5 with the valve of the present invention in another position thanthat shown in FIG. 5; and

PEG. 8 is a fragmentary sectional view taken along line 8-8 of FIG. 7.

Referring now to the drawings, and especially FIG. 1 thereof, a casing10 having having an upper casing head or flange 11 is shown inserted ina well bore 12 and having a lower terminus in a subterranean oilreservoir 13. Interiorly of the casing 10 is a tubing string 14, thelower end of which is connected to a conventional reciprocating pump 15which, in the present instance, is positioned in the oil reservoir 13.At the upper end of the tubing stiring 14 is a tubing head 16, an oildischarge pipe 17, and a solvent and air bleeder pipe 18 with valves 17aand 18a respectively therein. Interiorly of the tubing string 14 andextending substantially coaxially therewith is a sucker rod 19 whichsucker rod connects the tubing head 16 with the reciprocating pump 15and permits operation of the pump in a conventional manner.

In accordance with the invention, a valve assembly 20 is positioned inthe tubing string 14 below the predetermined and calculable area ofaccumulation of the paraffin interiorly of the tubing string 14, wherebyupon closing off of the oil outlet pipe 17 by the valve 17a andoperating of the reciprocatory pump with the valve 18a closed, asutlicient pressure is built up interiorly of the valve whichautomatically dumps the oil, or a certain set portion thereof, in thetubing string above the valve into the space intermediate the tubingstring 14 and the casing 10. The pump 15 is then shut down. Upon therelease of the oil in the tubing string superimposed above the valve 20,or any predetermined portion as preset, the valve 20 automaticallycloses, trapping a certain amout of oil above the valve in the tubingstring. At this point the valve 18a, which has associated therewith anair bleeder check valve (not shown) to admit atmospheric pressure intothe tubing string above the oil as it is dumped, is opened and a solventor the like placed into the tubing string 14. In a short period of timethe solvent causes dissolving of the paraffin, tars or basic sedimentswhich have been deposited and built up interiorly of the tubing andabove the valve 20.

To this end, and as best illustrated in FIGS. 2, 4, 5, and 6, the valve20 is provided with tubing coupling means 21 and 22 for mounting atubular body 23 in the tubing string While permitting fluidcommunication therethrough as by the bore 24 interiorly of the body 23.

The operating portion of the valve which permits dumping of the oil inthe tubing string upon a pre determined overpressure being reachedtherein, and which permits closing off of the valve upon dumping of thefluid into the casing and at a predetermined pressure, is best shown inFIGS. 2 and 5. As shown in FIG. 2, the body 23 is provided with a bore25 having an oil inlet 26 at one end therefiof which permitscommunication of the bore with the interior of the tubing via the bore25 of the valve body 23. Mounted interiorly of the bore 25 is a piston27 and at the lower end thereof a valve plug or disc 28 with, in thepresent instance, a conical seating portion 2 for seating in anextension 30 of the inlet 26. As shown in FIG. 5, the seating crosssectional area of the valve plug or disc 28, designated A-l for purposesof identification, is less than the cross sectional area of the piston27, which area is designated A2. Aligned with the piston 27 and normallybiasing the disc 28 into the closed position is biasing means, in thepresent instance a main piston spring 31, the upper portion of whichabuts an adjusting screw 32 (see FIG. 2). As illustrated in FIG. 5, themain piston 27 is provided with a shoulder stop 33 which prevents, uponthe piston being displaced vertically in the bore 25, verticaloverriding of the piston. Upon sufiicient pressure being applied to theinlet 26 and thus the area A-l of the plug 29, the plug moves ofi itsseat and the pressure at the inlet reaches the larger area A-2, thuscausing the piston to raise against the spring.

In order to dump the oil contained in the tubing string 11 above thevalve 20 and to hold the piston open against the spring 31, outlet meansfor dumping the oil in the tubing string is provided to dump the oilinto the casing while piston engaging means are provided to engage andhold the piston 27 until a predetermined low pressure is reached atwhich time the piston is permitted to move downwardly and the plug 29 toreseat in the seat of the inlet extension 30. To this end, and as bestillustrated in FIGS. 6, 7, and 8, at least one outlet means, in thepresent instance two outlets 34 are provided which permit communication,when the piston 27 is in its raised or elevated position, with the bore25 and thus the inlet 26, the outlets connecting and permitting thedumping of the oil in the tubing string above the valve into the spacebetween the tubing 14 and the casing 10.

To permit the piston to be held in the elevated position to allowcommunication between the inlet 26 and the outlets 34 until a preset lowpressure corresponding to a fixed amount of oil remaining in the tubingstring is left, the piston 27 is provided with engagement means, in thepresent instance an annular groove 35 which permits engage ment ofpressure responsive detent means 36, located on either side of thepiston and which engage the engagement means and hold the piston in anelevated position. As illustrated in FIG. 6, each of the detent means 36comprises a ball 37 lying in rubbing engagement with the piston 27, aball piston 38 and a grease-filled conduit 39 fitted with a diaphragm40. The opposite side of the diaphragm communicates with the bore 24 ofthe valve 20 thus causing the movement of the ball pistons to beresponsive to changes in internal pressure in the tubular valve body 23.The purpose in filling the conduit 39 with grease instead of allowingdirect communication of the oil with the base of the ball pistons 38 isto avoid, as much as possible, corrosive contact with the oil, which maycontain sulphur and water and other impurities. Such impurities, becauseof their corrosive effect, may deleteriously affect the operation of thevalve. As illustrated in FIGS. 7 and 8, as the piston 27 raises againstthe spring pressure 31, the outlets 34 permit dumping of the oil intothe casing 10, while the pressure existing at the inlets 41, causesinward deflection of the diaphragm and thus of the ball pistons. Thiscauses placement of the balls into the annular groove 35, when thepiston 27 raises to a position wherein the groove aligns with the balls.At a predetermined pressure, depending upon the setting of the detentmeans 36, the spring pressure of the spring 31 will overcome the piston27 and the detent means 36 and permit the piston 27 to reseat in theinlet extension 30.

It should be kept in mind that each oil well is different and that thevalve as heretofore described may be placed in the tubing stringanywhere from 500 to 5,000 feet below the earths surface. In addition,it has been found that the valve spring pressures should be designed sothat an overpressure of from 200 to 350 p.s.i. imposed on the statichead in the tubing string 14 will cause the valve to operate while a lowpressure of approximately 50 to 200 p.s.i. will cause the valve toreseat. In any event, the valve may be set to close with from to 600feet of oil remaining in the tubing string as the low pressure settingis proportional to the depth at which the valve is placed and inverselyas the weight of the pumped oil.

As will be known to those skilled in the art, the areas and springpressures of the various components of the valve 20 as heretoforedescribed may vary from well to well and the depth at which the valve 20is placed. Generally, it has been found that a ratio between the areasA-1 and A-2 of approximately 1:6 or a value of A1 equal to 16 to 20% ofA2 achieves the desired result, above described, and which providesparameters for spring compression design. Obviously, the adjustment ofthe spring compression by the adjusting screw 32 is dependent primarilyupon the location of the lower portion or bottom of the paratlin zoneand the specific gravity of the oil being pumped.

In practice, the valve is preferably placed at a depth of 400 to 500feet below the bottom of the paraffin zone and thus the desired valvepressure setting will be the static pressure at a point 400 to 500 feetbelow this region and may be determined roughly from the followingequation:

Valve pressure setting in p.s.i.=(D+400) S.G. .433

where D valve installation depth from ground level S.G.=specific gravityof the petroleum.

Thus for example if the lowest point at which paraffin accumulates is1500 feet below the surface, and assuming the valve is positioned in thetubing string 2000 feet below the surface level, the valve should be setto open at approximately 1000 to 1200 p.s.i. If the valve is set toclose at between and p.s.i., approximately 200 to 280 feet of oil wouldbe located in the tubing string above the valve. Thereafter of coursethe solvent would be applied and allowed to remain for a sufiicientperiod to dissolve the paraffin and then pump it out.

Thus a novel valve assembly is provided by the present invention forplacement in the tubing string which valve permits the removing ofparaifin deposits accumulated in the string without the necessity forpulling the tubin string or sucker rod for cleaning, thus providing theeconomic gain of minimum downtime. In addition, a novel method ofdissolving the paraffin in the paraifin region is provided wherein apredetermined amount of oil above the valve may be dumped into thecasing for placement in the tubing string of paraflin dissolvingsolvents.

Although the invention has been described with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction, method of operation, and the combination and arrangementof parts may be made without departing from the spirit and the scope ofthe invention as hereinafter claimed.

What is claimed is:

1. A method of dissolving paraffin from paraffin deposits accumulated ina tubing string mounted interiorly of a Well casing, said tubing havingmeans connected thereto for moving oil up said tubing out of asubterranean oil reservoir, said method comprising the steps of:providing a valve in said tubing string, said valve being responsive topressure and having a first position opening said tubing string to saidwell casing and a second position closing said valve to said wellcasing; closing off said tubing string above said valve; pumping anoverpressure into said tubing string, below the point of closure, untilsaid valve reaches its first or open position; reducing the overpressurein said tubing and permitting at least a portion of the oil in saidstring above said valve to flow into said casing until said valve closesOE; and thereafter injecting a parfiin solvent into said tubing stringthereby dissolving the paraflin accumulated therein.

2. A method in accordance with claim 1 including the step of, at thetime of insertion of said tubing string into said well casing,positioning said valve below the predetermined region wherein paraflindeposits accumulate.

3. A method in accordance with claim 1 wherein said step of reducing theoverpressure in said tubing includes the step of shutting down saidmeans for moving oil up said tubing after said valve reaches its open orfirst position.

4. A method of dissolving paraffin deposits in a tubing string mountedsubstantially coaxially with a well casing, said tubing string having apump connected at the lower end thereof and a sucker rod connected tosaid pump and connected above ground to a tubing head for moving oil upsaid tubing out of a subterranean oil reservoir; said method comprisingthe steps of: positioning a valve in said tubing string below thepredetermined region wherein paraffin deposits accumulate; said valveproviding an opening between the interior of said tubing and said wellcasing upon a predetermined overpressure occurring in said tubingstring; and closing said opening upon a preset and determined lowerpressure occurring in said tubing string; closing off the upper portionof said tubing string above said predetermined region while continuingto operate said pump to create an overpressure in said tu bing stringuntil said valve opens, and thereafter shutting down said pump;permitting at least a portion of the oil in said string above said valveto flow into said casing until said valve closes off; and injecting aparafiin solvent into said tubing string and keeping said solventtherein until said paraflin dissolves.

5. A system for dissolving parafiin from paraflin deposits accumulatedin a pressure assisted oil well; said oil well comprising a well casinghaving mounted therein and substantially coaXially therewith a tubingstring; an oil reservoir adjacent the lower terminal end of said wellcasing and a pump connected to said tubing string at the lower endthereof in said oil reservoir; means operable from the surface foractuating said pump; a pressure actuated valve in said tubing string;and means to restrict the flow of oil up said tubing string; said valvehaving means responsive to an increase in pressure in said tubing stringto permit dumping of oil from said string through said valve and intosaid casing, and responsive to a decrease in pressure to close saidvalve off to stop said dumping at a predetermined pressure substantiallybelow the pressure required to open said valve, whereby a solvent may beinjected into said tubing string to clean said string of accumulatedparaflin or other deposits therein.

References Cited UNITED STATES PATENTS 2,300,348 10/1942 Dana 166-41 X2,431,769 12/1947 Parker 137-469 2,704,979 3/1955 Van Willigen 166-41 X2,795,238 6/1957 Hirsch 251-94 X 3,014,531 12/1961 Weaver 166-413,018,786 1/1962 Stratton 137-118 3,102,590 9/1963 Grounds 166-224 X3,169,587 2/1965 Hubbard 166-224 X CHARLES E. OCONNELL, PrimaryExaminer. IAN A. CALVERT, Examiner.

